An X-ray image intensifier tube of this kind is known from U.S. Pat. No. 4,447,721. A tube disclosed therein comprises, accommodated in an envelope having an entrance window and an exit window, an entrance screen provided with an entrance luminescent layer and a photocathode and an exit screen provided with a phosphor layer. Using a potential difference between the photocathode and the phosphor layer, a photoelectron beam is projected onto the exit screen in intensified form. The intensification is realized by electron acceleration. The entrance screen and the exit screen have substantially the same surface area in the described proximity tube. Even though the length of such an X-ray image intensifier tube is substantially reduced with respect to a tube comprising an imaging electron optical system, such an advantage is substantially lost again because, in the case of non-direct visual observation, an adequately efficient optical transfer of an exit image having a comparatively large surface area to, for example, a television pick-up tube, requires a comparatively great length. As opposed to direct visual observation, a further conversion of an optical image into an electronic image is also necessary.